Drying drum



April 9, 1966 R. P. BROWN 3,246,400

DRYING DRUM Filed June 25, 1962 I N VEN TOR. fl/cA/Apo PB/POWN .4 rram/5k.

United States Patent 3,246,400 DRYING DRUM Richard P. Brown, Monrovia,Calif., assignor, by mesne assignments, to Bell & Howell Company,Chicago, Ill., a corporation of Illinois Filed June 25, 1962, Ser. No.204,930 7 Claims. (Cl. 34-110) This invention relates to an improveddrying drum, and particularly to a drying drum adaptable for use indynamic recording systems.

Dynamic recording systems, such as a recording system wherein aphotosensitive recording medium is employed to record images produced byan oscillograph, normally require a very short access time. The termaccess time is used to indicate the time interval between the exposureofthe photosensitive medium, which may be referred to as recordingpaper, to a light stimulus to be recorded, and the presentation of therecorded record for visual observation. Normally, a dynamic recordingsystem wherein a drying drum is utilized includes apparatus wherein therecording paper, which is in the form of an elongated strip, is passedthrough a plurality of baths of developing solutions after exposure.After passing through the baths, the recording paper is placed intocontact with a rotating drying drum for drying of the developingsolutions. The drying drum is heated internally, and is arranged torotateat such speed with relation to the speed of the strip of recordingpaper that there is no relative movement between the moving surface ofthe drying drum and the moving recording paper. After drying, therecording paper is passed from the apparatus for visual observation.

Heretofore, drying drums for use in such apparatus have comprised acylindrical platen made of stainless steel, arranged to be engageablewith the recording paper. The surface of such drying drums was smooth.Several problems have impaired satisfactory performance of these formerdrying drums.

Although the internal heating means are arranged to distribute the heaton the interior surface of the platen as evenly as possible, it isimpossible to apply heat equally to all points on the platen. For-merplaten'constructions have comprised a relatively thin layer of amaterial such as stainless steel, which does not have a high coefficientof thermal conductivity. As a result, considerable diiferences intemperature have resulted over the platen surface, due to the inabilityof such thin layer of material to conduct heat laterally about theplaten to equalize surface temperature. It is a characteristic of therecording paper ordinarily used with such systems that the papercontracts when dried, and the extent of such contraction is dependentupon the heat applied to the paper during drying. The non-uniformheating of the surface has therefore aifected the recording paperdimensionally, resulting in undesirable differences in the width of thepaper throughout the length of the record.

A more serious problem has existed due to the formation of a boundarylayer of air and steam between the paper and the platen surface as thewet paper comes into contact with the heated platen. The formation ofsuch boundary layer causes a loss of intimate contact between the paperand the platen surface, and a corresponding reduction in the amount ofheat transferable from the platen to the paper. The boundary layer hasbeen found to occur at paper speeds of approximately ten feet perminute, and former dynamic recording systems of the type described havethereby been limited to paper speeds of ten feet per minute, or less,over the drying drum. The remainder of the dynamic recording system iscapable of producing a record at a much higher speed, and thus thedefects of former drying drums have reduced the effectiveness of theentire apparatus.

3,246,400 Patented Apr. 19, 1966 Certain dynamic recording systems whichdo not employ developing baths, and therefore concern themselves withsubstantially smaller quantities of developing solutions to be driedfrom the paper, include a stationary platen rather than a drying drum.Where a platen is stationary, it has been possible to provide largeslots in the platen which scrape oif the boundary layer of air and steamas the paper moves across the platen, in order to insure intimatecontact between the platen and the paper. Such slots have beenimpractical, however, in systems wherein there is no relative motionbetween the platen and the moving paper, for the reason that the'portionof the recording paper adjacent the large slot remains unheated and,therefore, undried. A permanent and undesirable impression is therebyleft on the recording paper.

This invention resolves the foregoing difficulties by the provision of adrying drum so constructed as to provide substantially uniformtemperature over the entire drum surface, and provided with means forventing the boundary layer of air and steam without the leaving ofundried areas upon the recording paper.

Briefly, this invention provides a drying drum of conventional outerdimensions made from a material having high heat conductivity. A thicklayer of such material is used in order to provide good lateralconduction of heat for substantially uniform surface temperature. It hasbeen found that within certain critical dimensions, very small groovesmay be provided upon the drum surface for venting of the boundary layerof air and steam. Such grooves are sufficiently small that the portionsof the paper adjacent the grooves absorb sufficient heat from thesurrounding paper and platen surface for satisfactory drying, especiallywhere substantially uniform temperature prevailson the platen surface.Furthermore, as the recording paper contracts during drying, certainportions of 'its surface will be moved from positions adjacent groovesto positions adjacent the platen surface between the grooves, if thegrooves are sufficiently small. Therefore, this invention provides adrum surface which defines a plurality of small parallel grooves. Eachgroove has a width of from 0.0005 inch to 0.002 inch, and the maximumdepth of each groove is substantially equal to its width. Each of thelands, which are the areas on the drum surface between the grooves, mustbe at least as wide as the width of each of the grooves. In order toprovide a sufficient total groove area for carrying off the air andsteam, the grooves are disposed along the drum surface at a frequency ofat least grooves per inch, but not more than 600 grooves per inch.

It has been found in practice that a drying drum in accordance with thepresent invention will permit drying of recording paper at speeds 'ashigh as fifty feet per minute. Such speeds may even exceed thecapabilities of the remainder of the apparatus for delivering developedpaper to be dried, but it has been found that satisfactory performanceof the entire apparatus may be achieved at speeds up. to thirty feet perminute. Thus the drying drum, according to the present invention, hastripled the output capacity of this type of dynamic recording system.

This invention will be more clearly understood with reference to thefollowing description and accompanying drawings, in which: 1

FIG. 1 is a perspective view of a drying drum in accordance with thepresent invention, partially cut away;

FIG. 2 is an enlarged partial cross-section view of the exterior surfaceof a drying drum in accordance with the present invention; and I FIG. 3is an enlarged cross-section view, partially cut away, of anotherembodiment of a drying drum in accordance with the present invention.

Referring now to the drawings, FIG. 1 shows a strip of photosensitiverecording paper 5 engaged with a drying drum indicated generally at 6,as a part of a dynamic recording system (not shown), wherein therecording paper 5 has been exposed to a source of light and. passedthrough a series of baths of developing solution. The recording paper 5has a path of movement in the direction of the arrows and is heldagainst the exterior surface of the drying drum 6, which exteriorsurface may be referred to as the platen 7, by guide roller 10. Guideroller is arranged at any desired location, and normally is at a pointmore than 180 around the platen 7 from the point where the recordingpaper 5 first engages the platen 7, in order to provide contact for asufiicient time for drying.

In the preferred form, the drying drum 6 is formed by a platen 7substantially in the shape of a hollow cylinder. The ends of the platen7 are closed by suitable end pieces 8 each containing a central shaft" 9or other suitable means for rotatably mounting the drying drum 6 Withinthe dynamic recording system (not shown). Heating means (not shown) aredisposed within the hollow interior of the drying drum 6, and arearranged to distribute heat as evenly as possible around the interiorsurface of the platen 7. In the preferred form, the platen'7 is madefrom a material having a high coeificient of thermal conductivity, suchas aluminum, and is of a suflicient thickness to insure good lateralthermal conduction around the circumference of the palten. In thepresently preferred embodiment, the platen 7 has a diameter of teninches, and is comprised of aluminum having a thickness of five-eighthsinch.

Referring now to FIG. 2, the exterior surface of the platen 7 defines aplurality of elongated grooves 11. The grooves 11 are disposedsubstantially equidistant from and parallel to one another. In thepreferred form, the

grooves 11 extend circumferentially around the drying drum 6 in the samedirection as the direction of movement of the recording paper 5.However, the grooves 11 may extend longitudinally or angularly in anydesired direction. The preferred circumferential direction for grooves11 is selected because such grooves may be quickly and inexpensivelyformed by lathe turning. V

In the dynamic recording system with which a drying drum in accordancewith the present invention is used, there is no relative motion betweenthe surface of the platen 7 and the surface of the recording paper 5.The

lower surface of the recording paper 5 is normally in intimate contactwith the platen 7, but, as illustrated in FIG. 2, a portion of therecording paper 5 directly adjacent the grooves 11 has no contact withthe heated platen 7. The size and frequency of placement of grooves 11therefore becomes critical for the reason that grooves 11 having toogreat a width will leave a permanent impression upon the portions of therecording paper 5 adjacent the grooves, which will be undried. V i

The purpose of the grooves is to provide a channel for carrying off theboundary layer of air and steam forming between the platen 7 and therecording paper 5 as the Wet recording paper 5 comes into contact withthe heated platen 7. There must, therefore, be a sufficient total groovearea for carrying oif all of the air and steam required to be carriedoff. For this reason, the selection of proper size and number for thegrooves 11 requires a balancing of the requirements for providing thedesired total groove area, and also providing the maximum possible areafor intimate contact between the recording paper 5 and the surface ofthe platen 7.

In the preferred embodiment of this invention, therefore, this properbalance is achieved by providing grooves 11 having a width in the rangeof from 0.0005 inch to 0.002 inch, and optimum results are obtained whenthe groove width is substantially 0.001 inch.

In order to provide the required total groove area, there must be alarge number of the grooves 11, and

it has been found that the frequency at which grooves 11 are disposedalong the surface of the platen 7 must be at least one-hundred fiftygrooves per inch, but not more than six-hundred grooves per inch. Thefrequency with which the grooves 11 are disposed is inverselyproportional to the width selected for the grooves. When grooves 11 areutilized having the optimum width of 0.001 inch, the optimum frequencyhas been found to be threehundred grooves per inch.

To provide the desired total area for intimate contact between therecording paper 5 and the surface of the laten 7, it is necessary thatthe lands, indicated generally at 12, be of at least the same width asthe width of the grooves 11. In the preferred form, the lands 12 are atleast twice the Width of the grooves 11.

In operation, the steam is forced by its own expansion and the pressureof the recording paper 5 against the lands 12 into the nearest groove11. As the drying drum 6 rotates, the steam in the grooves 11 passes outof the grooves 11 in the area between take-up roller 10 and the pointwhere the recording paper 5 first engages the drying drum 6. No boundarylayer is permitted to form, and the recording paper 5 is permitted toabsorb heat from the platen 7 through the lands 12 substantiallyuniformly over the entire outer surface of the platen '7.

In the event chemicals are employed in the recording paper 5, or in thedeveloping baths (not shown) which would be corrosive to the materialfrom which the platen 7 is made, a thin layer of a non-corrosivematerial may be placed over the outer surface of the platen 7. Such anembodiment is shown in FIG. 3, wherein the platen 7A is comprised of asubstantially thick layer of a material 14 which is a good thermalconductor, to the exterior of which is bonded a thin layer ofcorrosion-resistant material 15, such as stainless steel. The grooves 11are formed in the exterior surface of the corrosion-resistant material15. In the preferred embodiment, the layer of corrosion-resistantmaterial is stainless steel having a thickness of approximately 0.015inch, in order that its characteristics of poor thermal conductivity donot impair the even heat distribution of the material 14 having a highcoefficient of thermal conductivity. The material 14 is aluminum in thepreferred embodiment, having a thickness of five-eighths inch for a 10inch diameter platen 7.

The invention claimed is:

1. Apparatus for drying elongated strips of photographic material of theclass wherein the strip of material to be dried is moving and is engagedwith the surface of a heated rotating drying drum which rotates about anaxis transverse to the path of motion of the strip at such speed thatthe surface of the drum travels at substantially the same rate of speedas the strip, so that there is substantially no relative motion betweenthe drum surface and the strip engaged therewith, an improved dryingdrum, comprising:

(a) a hollow cylindrical drum having closed ends and adapted to carryinternal heating means,

(b) the drum being made from a material having a coefficient of thermalconductivity and having a wall thickness suflicient to provide asubstantially uniform temperature at all points on the cylindrical drumsurface,

(0) the drum having a plurality of substantially identical parallelgrooves on its exterior surface, the grooves being equidistant from oneanother and separated by a distance at least as great as the width ofeach groove,

(d) the Width of each groove being in the range of from 0.0005 inch to0.002 inch, and the maximum depth of each groove being substantiallyequal to its width,

(e) the parallel grooves being disposed at a frequency in the range offrom to 600 grooves per inch along the surface of the platen.

2. A drying drum according to claim 1 wherein the width of each grooveis at least 0.001 inch and the grooves are disposed along the platensurface at a frequency of at least three-hundred per inch.

3. A drying drum according to claim 1 wherein the width of each grooveis at least 0.001 inch and the distance between adjacent grooves is atleast twice the width of each groove.

4. A drying drum according to claim 1 wherein the grooves extendtransverse to the axis of the drum, in the same direction as the path ofmovement of the strip of material being dried.

5. A drying drum according to claim 1 wherein the drum has a thin layerof a corrosion-resistant metal thermally bonded to the exterior surfaceof a thick layer of a material having a high coefficient of thermalconductivity, and the grooves are formed in the exterior surface of thethin layer of corrosion-resistant metal.

6. Apparatus for drying elongated strips of photographic material of theclass wherein the strip of material to be dried is moving and is engagedwith the surface of a heated rotating drying drum which rotates about anaxis transverse to the path of motion of the strip at such speed thatthe surface of the drum travels at substantially the same rate of speedas the strip, so that there is substantially no relative motion betweenthe drum surface and the strip engaged therewith, the apparatuscomprismg (a) a hollow cylindrical drum adapted to carry internalheating means and made from a material having a coefiicient of thermalconductivity and a wall thickness sufficient to provide conduction ofheat laterally in the wall of the drum for maintaining a substantiallyuniform temperature over the cylindrical drum surface engaged by thestrip of material,

(b) the drum having a plurality of substantially identical parallelgrooves on its exterior surface, the grooves being equidistant from oneanother and separated by a distance at least as great as the width ofeach groove,

(c) the width of each groove being in the range of from 0.0005 inch to0.002 inch, inclusive, and the maximum depthof each groove beingsubstantially equal to its width,

(f) the parallel grooves being disposed at a frequency in the range offrom 150 to 600 grooves per inch, inclusive, along the surface of theplaten, and

(e) means for maintaining a wet shrinkable strip of photographicmaterial in intimate contact with the exterior surface of the drum overa selected extent circumferentially of the drum as the drum is rotated,

(1) the portions of the photographic material in contact with the drumbetween the grooves being dried by heat transferred from the drum,

(2) the portions of the photographic material spanning the grooves beingdried by heat transferred thereto from the portions of the material incontact with the drum between the grooves,

(3) water vapor released from the material passing away from thematerial through the grooves,

(4) the photographic material within the selected extent of the drumthereby being maintained at substantially uniform temperature so that itshrinks substantially uniformly in a direction transverse to its path ofmotion.

7. Apparatus for drying a strip of wet photographic material ofindeterminant length, comprising (a) a rotatable heated drum having acircularly cylindrical exterior surface maintained at a selectedtemperature substantially uniformly thereover,

(b) means for intimately engaging the wet strip with the drum around aportion of the periphery of the drum,

the strip shrinking as it dries in proportion to the heat appliedthereto,

(c) the surface of the drum engaged by the strip defining a plurality ofsmall closely-spaced grooves and lands for receiving and directing awayfrom the strip vapors produced as the strip is dried,

the grooves being disposed and arranged on the drum so that the strip ismaintained at substantially uniform temperature along lines transverseto its length so that the strip shrinks uniformly transversely of itslength and the lands having a width at least twice the width of thegrooves.

References Cited by the Examiner UNITED STATES PATENTS 2,299,662 10/1942Thaler 34-122 2,519,105 8/1950 Blue 341 10 2,621,982 12/1952 Crosland34-110 2,861,508 11/1958 Baumbach 34--155 FOREIGN PATENTS 872,3 62 7/1961 Great Britain.

WILLIAM F. ODEA, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

7. APPARATUS FOR DRYING A STRIP OF WET PHOTOGRAPHIC MATERIAL OFINDETERMINANT LENGTH, COMPRISING (A) A ROTATABLE HEATED DRUM HAVING ACIRCULARLY CYLINDRICAL EXTERIOR SURFACE MAINTAINED AT A SELECTEDTEMPERATURE SUBSTANTIALLY UNIFORMLY THEREOVER, (B) MEANS FOR INTIMATELYENGAGING THE WET STRIP WITH THE DRUM AROUND A PORTION OF THE PERIPHERYOF THE DRUM, THE STRIP SHRINKING AS IT DRIES IN PROPORTION TO THE HEATAPPLIED THERETO, (C) THE SURFACE OF THE DRUM ENGAGED BY THE STRIPDEFINING A PLURALITY OF SMALL CLOSELY-SPACED GROOVES AND LANDS FORRECEIVING AND DIRECTING AWAY FROM THE STRIP VAPORS PRODUCED AS THE STRIPIS DRIED, THE GROOVES BEING DISPOSED AND ARRANGED ON THE DRUM SO THATTHE STRIP IS MAINGAINED AT SUBSTANTIALLY UNIFORM TEMPERATURE ALONG LINESTRANSVERSE TO ITS LENGTH SO THAT THE STRIP SHRINKS UNIFORMLYTRANSVERSELY OF ITS LENGTH AND THE LANDS HAVING A WIDTH AT LEST TWICETHE WIDTH OF THE GROOVES.